Tissue Harmonic Imaging in comparison to conventional sonography: Influence on image quality and observervariability in the intima-media thickness measurements of the common carotid artery.

Objective: The purpose of this study was to determine if tissue harmonic im aging (THI) produced a higher image quality than conventional sonography an d if THI reduced the observer availability in the intima media thickness (I MT) measurements of the common carotid artery (ACC). Subjects and methods: A prospective study was performed on 26 healthy volunteers and IMT was asse ssed by three experienced sonographers in 52 carotid arteries. A 7.5 MHz tr ansducer was used to measure carotid IMT in both harmonic and fundamental m odes. Three measurements of IMT were carried out on the far wall of the ACC along a 1 cm-long section proximal to the bifurcation. Image quality was g raded from 1 - 3 (1 = excellent, 2 = good, 3 = poor). IMT measurements usin g harmonic and fundamental modes were compared and intra- and interobserver variability were calculated. Statistical analyses were performed using a k appa analysis, ANOVA and the McNemar/ Wilcoxon Test. Results: In the 52 cas es image quality was excellent in 51% using THI in comparison to 32% using conventional sonography. Image quality was graded significantly more freque nt as excellent using harmonic sonography as compared to conventional sonog raphy (p = 0.001). A significant difference in IMT was found between the me asurements obtained by harmonic imaging in comparison to those obtained by conventional imaging (p < 0.0001). Using the harmonic mode inter-observer v ariability of the IMT measurements was significantly reduced from 8.1% to 5 .2% (p < 0.001). Conclusions: THI produced a higher image quality with a be tter visualisation of carotid IMT and reduced significantly the intra- and inter-observer variability in the IMT measurements.